The series of studies to be carried out on attentional control attempt to distinguish between two visual subsystems--one subserving the control of selective visual attention and one subserving explicit stimulus identification--in three neurologic populations. It has been hypothesized that these visual processes can be distinguished functionally as well as anatomically. The present proposal seeks to confirm this hypothesis by studying residual function in patients with focal parietal or occipital brain lesions that selectively disrupt one visual subsystem, and contrasting this performance with that of commissurotomy patients in whom both subsystems are intact but dissociable. The proposed studies make use of facilitation paradigms recently developed in the field of cognitive psychology. By bringing these research methods to bear on neurologic populations we hope to isolate the capabilities of each visual subsystem as well as reveal ways in which they may be interdependent. In addition, these paradigms will be modified in order to explore oculomotor and praxic components associated with changes in the locus of visual attention.